A Microwave Scattering Database of Oriented Ice and Snow Particles: Supporting Habit-Dependent Growth Models and Radar Applications (McRadar 1.0.0)

Abstract. The optical properties of atmospheric hydrometeors are a crucial component of any forward operator. These forward operators are essential data assimilation, and atmospheric model evaluations. Recent advances in microphysical modelling, such as Lagrangian super-particle models with habit prediction for ice particles, allow for the continuous evolution of particle properties in contrast to fixed hydrometer classes with fixed properties. This increasing complexity demands scattering databases capable of handling a wide range of particle properties.

The discrete dipole approximation (DDA) is one of the most accurate and widely used methods for computing the scattering properties of irregular ice particles. However, its high computational cost typically limits either the diversity of particle shapes or the range of environmental parameters (e.g., frequency, temperature) represented in existing databases, constraining their applicability to models with highly variable microphysics.

In this study, we present a new DDA-based database of optical properties at 5.6, 9.6, 35.6, and 94 GHz, specifically designed to accommodate the broad range of ice crystal morphologies predicted by habit-evolving schemes. The database contains 2,627 individual ice crystals, including dendrites, plates, and columns, as well as 450 aggregates with varying degrees of riming and crystal types. The data are organized in three levels: Level 0 provides raw scattering matrices at individual orientations for a full range of scattering angles; level 1a summarizes Mueller and amplitude matrix elements relevant for radar applications (at forward and backward scattering angles); and level 1b offers lookup tables of scattering properties that are relevant for polarimetric radars assuming azimuthally random orientations of the particles. These data allow for flexible treatment of the canting angle of the particles. The lookup tables are directly accessible via the McRadar simulator and can also be interfaced with other forward operators.

The new database allows for a more consistent and realistic treatment of evolving ice particle properties in atmospheric models, improving the interpretation of radar observations and model-observation integration.